CN117517429A

CN117517429A - Gas sensor and method for grasping deviation of reference potential of gas sensor

Info

Publication number: CN117517429A
Application number: CN202310906739.8A
Authority: CN
Inventors: 田中信伍; 渡边悠介; 桥川凌
Original assignee: NGK Insulators Ltd
Current assignee: NGK Insulators Ltd
Priority date: 2022-08-05
Filing date: 2023-07-24
Publication date: 2024-02-06
Also published as: DE102023119763A1; US20240044835A1; JP2024022007A

Abstract

The invention provides a gas sensor and a method for grasping deviation of reference potential of the gas sensor. A gas sensor (100) is provided with a sensor element (101) and a control device (95) and detects a specific gas concentration, which is a specific gas concentration in a gas to be measured. A sensor element (101) is provided with: a device body (layers (1-6)) having a solid electrolyte layer having oxygen ion conductivity, and provided with a gas flow section for introducing and flowing a gas to be measured therein; a measurement electrode (44) disposed in a third internal cavity (61) in the measured gas flow section; and a reference electrode (42) which is disposed inside the element body so as to be in contact with a reference gas that is a detection reference for a specific gas concentration. A control device (95) measures the voltage (Vrg) between the ground and the reference electrode (42), and based on the voltage (Vrg), grasps the potential of the reference electrode (42), that is, the deviation of the reference potential.

Description

Gas sensor and method for grasping deviation of reference potential of gas sensor

Technical Field

The present invention relates to a gas sensor and a method for grasping a deviation of a reference potential of the gas sensor.

Background

Conventionally, a gas sensor for detecting the concentration of a specific gas such as NOx in a measured gas such as an automobile exhaust gas has been known. For example, the sensor element of the gas sensor described in patent document 1 includes: a laminate having a plurality of solid electrolyte layers having oxygen ion conductivity, and provided with a gas to be measured flowing portion in which a gas to be measured is introduced and circulated; a measurement electrode disposed in the measured gas flow section; a gas-to-be-measured side electrode disposed in a portion of the laminate exposed to the gas to be measured; a reference electrode disposed inside the laminate; and a porous reference gas introduction layer for introducing a reference gas (for example, atmospheric air) serving as a reference for detecting a specific gas concentration of the gas to be measured, and flowing the reference gas through the reference electrode. In this gas sensor, a specific gas concentration in a gas to be measured is detected based on an electromotive force generated between a reference electrode and a measurement electrode. The gas sensor further includes a reference gas adjustment mechanism for flowing a control current between the reference electrode and the electrode on the gas side to be measured, and sucking oxygen into the periphery of the reference electrode. Patent document 1 describes: by the reference gas adjusting mechanism sucking oxygen into the periphery of the reference electrode, when the oxygen concentration of the reference gas in the periphery of the reference electrode is temporarily reduced, the reduction in the oxygen concentration can be compensated for, and the reduction in the detection accuracy of the specific gas concentration can be suppressed.

Prior art literature

Patent literature

Patent document 1: japanese patent application laid-open No. 2018-173320

Disclosure of Invention

However, even in the case where oxygen is inhaled around the reference electrode using the reference gas adjustment mechanism as in the gas sensor described in patent document 1, it is difficult to keep the oxygen concentration around the reference electrode completely constant. If the oxygen concentration around the reference electrode changes, the potential of the reference electrode changes, resulting in a decrease in the detection accuracy of the specific gas concentration. Therefore, it is desirable to grasp the deviation of the potential of the reference electrode.

The present invention has been made to solve the above-described problems, and its main object is to grasp the deviation of the reference potential.

The present invention adopts the following means to achieve the above-described main object.

[1] The gas sensor of the present invention comprises a sensor element and a control device, and detects a specific gas concentration, that is, a specific gas concentration in a measured gas,

the sensor element is provided with:

a device body having a solid electrolyte layer having oxygen ion conductivity, and having a measured gas flow portion for introducing and flowing the measured gas therein;

A measurement electrode disposed in a measurement chamber of the measurement target gas flow section; and

a reference electrode disposed in the element body so as to be in contact with a reference gas that is a detection reference of the specific gas concentration,

the control device measures a voltage between the ground and the reference electrode, and grasps a potential of the reference electrode, that is, a deviation of the reference potential, based on the measured voltage.

In this gas sensor, the control device measures the voltage between the ground and the reference electrode. This voltage changes with a change in the oxygen concentration around the reference electrode, that is, a change in the reference potential, which is the potential of the reference electrode, and therefore, the deviation of the reference potential can be grasped based on this voltage.

In this case, the control device can grasp the deviation of the reference potential by comparing the measured value of the voltage between the ground and the reference electrode with the normal value or the allowable range. Specific examples of grasping the reference potential include: and comparing the measured value with a normal value or an allowable range, and calculating a value indicating a deviation of the reference potential based on the measured value. More specifically, there may be mentioned: the comparison of the magnitude relation between the measured value and the normal value, the calculation of the difference or the ratio between the measured value and the normal value, the judgment of whether the measured value is within the allowable range, and the like. The control device can grasp the deviation of the reference potential by performing 1 or more of these schemes.

[2] The gas sensor (the gas sensor according to [1 ]) may be: the sensor element includes a reference gas adjustment pump unit configured to include: the control device controls the reference gas adjustment pump unit so as to suck oxygen from the periphery of the reference electrode to the periphery of the measured gas side electrode when the measured voltage is greater than an allowable range, and controls the reference gas adjustment pump unit so as to suck oxygen from the periphery of the measured gas side electrode to the periphery of the reference electrode when the measured voltage is less than the allowable range. Accordingly, the oxygen concentration around the reference electrode can be adjusted according to the deviation of the reference potential, and therefore, the deviation of the reference potential can be made small, and the degradation of the detection accuracy of the specific gas concentration can be suppressed. The control device determines whether or not the measured voltage is greater than the allowable range as follows: for example, the measured voltage may be compared with an allowable range, or the deviation amount of the reference potential obtained based on the measured voltage may be compared with an allowable range.

[3] The gas sensor (the gas sensor according to [1] or [2 ]) may be: the sensor element includes a measurement pump unit configured to include: the control device performs a measurement pump control process of controlling the measurement pump unit so that a voltage between the measurement electrode and the reference electrode, that is, a measurement voltage reaches a measurement voltage target value, and detects the specific gas concentration in the measurement gas based on a pump current flowing through the measurement pump unit due to the measurement pump control process, and the control device corrects the control of the measurement pump unit in the measurement pump control process based on a deviation of the grasped reference potential. Accordingly, even if the reference potential is deviated, the detection accuracy of the specific gas concentration can be suppressed from being lowered by correcting the control of the measurement pump unit.

[4] The gas sensor (the gas sensor according to [3] above) may be: the sensor element includes an adjustment pump unit configured to include: the control device performs an adjustment pump control process of adjusting the oxygen concentration in the oxygen concentration adjustment chamber by controlling the adjustment pump means so that the voltage between the inner adjustment electrode and the reference electrode, that is, the adjustment voltage, reaches an adjustment voltage target value, at an inner adjustment electrode disposed in the measured gas flow portion in the oxygen concentration adjustment chamber upstream of the measurement chamber, and corrects the control of the adjustment pump means in the adjustment pump control process based on the deviation of the grasped reference potential. Accordingly, when the reference potential is deviated, not only the control of the measurement pump unit but also the control of the adjustment pump unit is corrected, and therefore, the decrease in the detection accuracy of the specific gas concentration can be further suppressed.

[5] The gas sensor (the gas sensor according to any one of [1] to [4 ]) may be: the sensor element includes a ground terminal connected to the ground, and the control device measures a voltage between the ground terminal and the reference electrode as a voltage between the ground and the reference electrode.

[6] The gas sensor (the gas sensor according to [5] above) may be: the sensor element includes a heater for heating the element body, and the ground terminal is a terminal of the heater.

[7] The method for grasping the deviation of the reference potential of the gas sensor according to the present invention is a method for grasping the deviation of the reference potential of the gas sensor for detecting the concentration of a specific gas among the measured gases, that is, the specific gas concentration,

the gas sensor is provided with a sensor element,

the sensor element is provided with:

a measurement electrode disposed in the measured gas flow section; and

the method for grasping the deviation of the reference potential of the gas sensor includes the steps of measuring a voltage between the ground and the reference electrode, and grasping the potential of the reference electrode, that is, the deviation of the reference potential, based on the measured voltage.

The grasping method can grasp the deviation of the reference potential in the same manner as the gas sensor described above. In this grasping method, various modes of the above-described arbitrary gas sensor (arbitrary gas sensor in [1] to [6 ]) may be adopted, and a step of realizing the functions of the above-described arbitrary gas sensor (arbitrary gas sensor in [1] to [6 ]) may be added.

Drawings

Fig. 1 is a schematic cross-sectional view of a gas sensor 100.

Fig. 2 is a schematic diagram showing the inside of the sensor element 101, the inside of the control device 95, and wiring between the sensor element 101 and the control device 95.

Fig. 3 is a block diagram showing an electrical connection relationship between the control device 95 and each unit and the heater section 70.

Fig. 4 is a flowchart showing an example of the reference potential adjustment process.

Fig. 5 is a flowchart showing an example of the control correction process.

Fig. 6 is a schematic cross-sectional view of a sensor element 201 according to a modification.

Detailed Description

Next, embodiments of the present invention will be described with reference to the drawings. Fig. 1 is a schematic cross-sectional view schematically showing an example of the structure of a gas sensor 100 according to an embodiment of the present invention.

Fig. 2 is a schematic diagram showing the inside of the sensor element 101, the inside of the control device 95, and wiring between the sensor element 101 and the control device 95. Fig. 3 is a block diagram showing an electrical connection relationship between the control device 95 and each unit and the heater 72. The gas sensor 100 is mounted on a pipe such as an exhaust pipe of an internal combustion engine such as a gasoline engine or a diesel engine. The gas sensor 100 detects the concentration of a specific gas such as NOx and ammonia in an exhaust gas of an internal combustion engine as a measurement target gas. In the present embodiment, the gas sensor 100 measures the NOx concentration as the specific gas concentration. The gas sensor 100 includes: a sensor element 101 having an elongated rectangular parallelepiped shape; each unit 15, 21, 41, 50, 80 to 83, which is configured to include a part of the sensor element 101; a heater section 70 provided inside the sensor element 101; and a control device 95 for controlling the entire gas sensor 100.

The sensor element 101 is an element having a laminate of zirconium oxide (ZrO ₂ ) The first substrate layer 1, the second substrate layer 2, the third substrate layer 3, the first solid electrolyte layer 4, the separator 5, and the second solid electrolyte layer 6 each having the oxygen ion conductive solid electrolyte layer formed thereon are laminated in this order. In addition, the solid electrolyte forming the six layers is a dense and airtight solid electrolyte. The sensor element 101 is manufactured by, for example, performing predetermined processing, printing of a circuit pattern, and the like on a ceramic green sheet corresponding to each layer, and then laminating the ceramic green sheets, and further advancing the laminated ceramic green sheetFiring is performed to integrate them.

The gas introduction port 10, the first diffusion rate control portion 11, the buffer space 12, the second diffusion rate control portion 13, the first internal cavity 20, the third diffusion rate control portion 30, the second internal cavity 40, the fourth diffusion rate control portion 60, and the third internal cavity 61 are formed adjacent to each other in a sequentially communicating manner between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4 on the distal end portion side (left end portion side in fig. 1) of the sensor element 101.

The gas inlet 10, the buffer space 12, the first internal cavity 20, the second internal cavity 40, and the third internal cavity 61 are internal spaces of the sensor element 101 provided so as to dig out the separator 5, wherein an upper portion of the internal spaces is defined by a lower surface of the second solid electrolyte layer 6, a lower portion is defined by an upper surface of the first solid electrolyte layer 4, and a side portion is defined by a side surface of the separator 5.

The first diffusion rate controlling section 11, the second diffusion rate controlling section 13, and the third diffusion rate controlling section 30 are each provided as 2 slits that are horizontally long (the direction perpendicular to the drawing forms the longitudinal direction of the opening). The fourth diffusion rate control portion 60 is provided as 1 slit (the longitudinal direction of the opening is formed in the direction perpendicular to the drawing) which is formed as a gap between the lower surface of the second solid electrolyte layer 6. The portion from the gas inlet 10 to the third internal cavity 61 is also referred to as a measured gas flow portion.

The sensor element 101 includes: a reference gas introduction portion 49 for allowing the reference gas to flow from the outside of the sensor element 101 to the reference electrode 42 when the NOx concentration is measured. The reference gas introduction portion 49 has a reference gas introduction space 43 and a reference gas introduction layer 48. The reference gas introduction space 43 is: a space provided inward from the rear end surface of the sensor element 101. The reference gas introduction space 43 is provided between the upper surface of the third substrate layer 3 and the lower surface of the separator 5, and the side portion is provided at a position partitioned by the side surface of the first solid electrolyte layer 4. The reference gas introduction space 43 is opened at the rear end surface of the sensor element 101, and the opening functions as an inlet portion 49a of the reference gas introduction portion 49. The reference gas is introduced into the reference gas introduction space 43 from the inlet portion 49 a. The reference gas introduction portion 49 applies a predetermined diffusion resistance to the reference gas introduced from the inlet portion 49a, and introduces the reference gas to the reference electrode 42. The reference gas is atmospheric air in the present embodiment.

The reference gas introduction layer 48 is provided between the upper surface of the third substrate layer 3 and the lower surface of the first solid electrolyte layer 4. The reference gas introduction layer 48 is: a porous body formed of a ceramic such as alumina. A part of the upper surface of the reference gas introduction layer 48 is exposed in the reference gas introduction space 43. The reference gas introduction layer 48 is formed to cover the reference electrode 42. The reference gas introduction layer 48 allows the reference gas to flow from the reference gas introduction space 43 to the reference electrode 42.

The reference electrode 42 is an electrode formed so as to be sandwiched between the upper surface of the third substrate layer 3 and the first solid electrolyte layer 4, and as described above, a reference gas introduction layer 48 connected to the reference gas introduction space 43 is provided around the reference electrode. As will be described later, the oxygen concentration (oxygen partial pressure) in the first internal cavity 20, the second internal cavity 40, and the third internal cavity 61 can be measured by the reference electrode 42. The reference electrode 42 is formed as a porous cermet electrode (e.g., pt and ZrO ₂ Metal ceramic electrode of (c).

In the measured gas flow portion, the gas inlet 10 is a portion that opens to the outside space, and the measured gas is introduced into the sensor element 101 from the outside space through the gas inlet 10. The first diffusion rate control section 11 is a portion that applies a predetermined diffusion resistance to the gas to be measured introduced from the gas introduction port 10. The buffer space 12 is a space provided for guiding the gas to be measured introduced from the first diffusion rate control unit 11 to the second diffusion rate control unit 13. The second diffusion rate control section 13 is a portion that applies a predetermined diffusion resistance to the gas to be measured introduced from the buffer space 12 into the first internal cavity 20. When the measured gas is introduced into the first internal cavity 20 from the outside of the sensor element 101, the measured gas is rapidly introduced into the sensor element 101 from the gas inlet 10 due to pressure fluctuation of the measured gas in the external space (pulsation of the exhaust pressure in the case where the measured gas is the exhaust gas of the automobile), but such measured gas is not directly introduced into the first internal cavity 20, but is introduced into the first internal cavity 20 after the pressure fluctuation of the measured gas is eliminated by the first diffusion rate control unit 11, the buffer space 12, and the second diffusion rate control unit 13. Thus, the pressure variation of the measured gas introduced into the first internal cavity 20 is almost negligible. The first internal cavity 20 is provided as a space for adjusting the partial pressure of oxygen in the gas to be measured introduced through the second diffusion rate control section 13. The main pump unit 21 operates to adjust the oxygen partial pressure.

The main pump unit 21 is an electrochemical pump unit including an inner pump electrode 22, an outer pump electrode 23, and a second solid electrolyte layer 6 sandwiched between the inner pump electrode 22 and the outer pump electrode 23, wherein the inner pump electrode 22 has a top electrode portion 22a provided on substantially the entire surface of a portion of the lower surface of the second solid electrolyte layer 6 facing the first internal cavity 20, and the outer pump electrode 23 is provided on a region of the upper surface of the second solid electrolyte layer 6 corresponding to the top electrode 22a so as to be exposed to an external space.

The inner pump electrode 22 is formed as: the solid electrolyte layer (the second solid electrolyte layer 6 and the first solid electrolyte layer 4) crossing the upper and lower sides of the first internal cavity 20 and the spacer layer 5 constituting the side wall. Specifically, the top electrode portion 22a is formed on the lower surface of the second solid electrolyte layer 6 constituting the top surface of the first internal cavity 20, the bottom electrode portion 22b is formed on the upper surface of the first solid electrolyte layer 4 constituting the bottom surface, and the side electrode portions (not shown) are formed on the side wall surfaces (inner surfaces) of the separator 5 constituting the two side wall portions of the first internal cavity 20 so as to connect the top electrode portion 22a and the bottom electrode portion 22b, whereby the tunnel-like structure is arranged at the arrangement position of the side electrode portions.

The inner pump electrode 22 and the outer pump electrode 23 are formed as porous cermet electrodes (e.g., containing 1% au)Pt and ZrO ₂ Metal ceramic electrode of (c). The inner pump electrode 22 that contacts the gas to be measured is formed of a material that reduces the reduction ability of the NOx component in the gas to be measured.

In the main pump unit 21, a desired pump voltage Vp0 is applied between the inner pump electrode 22 and the outer pump electrode 23, and the pump current Ip0 is caused to flow between the inner pump electrode 22 and the outer pump electrode 23 in the positive or negative direction, whereby oxygen in the first internal cavity 20 can be sucked into the external space or oxygen in the external space can be sucked into the first internal cavity 20.

In order to detect the oxygen concentration (oxygen partial pressure) in the atmosphere of the first internal cavity 20, an electrochemical sensor unit, that is, a main pump control oxygen partial pressure detection sensor unit 80 is configured by the inner pump electrode 22, the second solid electrolyte layer 6, the separator 5, the first solid electrolyte layer 4, the third substrate layer 3, and the reference electrode 42.

The oxygen concentration (oxygen partial pressure) in the first internal cavity 20 is obtained by measuring the electromotive force (voltage V0) of the main pump control oxygen partial pressure detection sensor unit 80. Further, the pump voltage Vp0 of the variable power supply 24 is feedback-controlled so that the voltage V0 reaches the target value, thereby controlling the pump current Ip 0. Thereby, the oxygen concentration in the first internal cavity 20 can be maintained at a predetermined constant value.

The third diffusion rate control section 30 is as follows: the measured gas after the first internal cavity 20 has controlled the oxygen concentration (oxygen partial pressure) by the operation of the main pump unit 21 is introduced into the second internal cavity 40 by applying a predetermined diffusion resistance to the measured gas.

The second internal cavity 40 is provided as follows: the oxygen partial pressure of the gas to be measured, which is introduced through the third diffusion rate control section 30 after the oxygen concentration (oxygen partial pressure) has been adjusted in the first internal cavity 20 in advance, is adjusted by the auxiliary pump unit 50. Accordingly, the oxygen concentration in the second internal cavity 40 can be kept constant with high accuracy, and therefore, in such a gas sensor 100, the NOx concentration can be measured with high accuracy.

The auxiliary pump unit 50 is: an auxiliary electrochemical pump unit comprising an auxiliary pump electrode 51, an outer pump electrode 23 (not limited to the outer pump electrode 23, as long as it is an appropriate electrode outside the sensor element 101), and the second solid electrolyte layer 6, wherein the auxiliary pump electrode 51 has a top electrode portion 51a provided substantially entirely on a portion of the lower surface of the second solid electrolyte layer 6 facing the second internal cavity 40.

The auxiliary pump electrode 51 is disposed in the second internal cavity 40 in the same tunnel-like structure as the inner pump electrode 22 previously disposed in the first internal cavity 20. That is, the top electrode portion 51a is formed on the second solid electrolyte layer 6 constituting the top surface of the second internal cavity 40, the bottom electrode portion 51b is formed on the first solid electrolyte layer 4 constituting the bottom surface of the second internal cavity 40, and side electrode portions (not shown) connecting the top electrode portion 51a and the bottom electrode portion 51b are formed on the two wall surfaces of the separator 5 constituting the side wall of the second internal cavity 40, respectively, so that the structure is a tunnel-like structure. The auxiliary pump electrode 51 is also formed of a material having reduced reducing ability for NOx components in the measured gas, similarly to the inner pump electrode 22.

In the auxiliary pump unit 50, a desired voltage Vp1 is applied between the auxiliary pump electrode 51 and the outer pump electrode 23, whereby oxygen in the atmosphere in the second internal cavity 40 can be sucked into the external space or oxygen can be sucked into the second internal cavity 40 from the external space.

In order to control the oxygen partial pressure in the atmosphere in the second internal cavity 40, an auxiliary pump electrode 51, a reference electrode 42, a second solid electrolyte layer 6, a separator 5, a first solid electrolyte layer 4, and a third substrate layer 3 constitute an electrochemical sensor unit, that is, an auxiliary pump control oxygen partial pressure detection sensor unit 81.

The auxiliary pump unit 50 pumps with a variable power supply 52, and the variable power supply 52 controls the voltage based on the electromotive force (voltage V1) detected by the auxiliary pump control oxygen partial pressure detection sensor unit 81. Thereby, the partial pressure of oxygen in the atmosphere within the second internal cavity 40 is controlled to a lower partial pressure that has substantially no effect on the NOx measurement.

At the same time, the pump current Ip1 is used to control the electromotive force of the main pump control oxygen partial pressure detection sensor unit 80. Specifically, the pump current Ip1 is input as a control signal to the main pump control oxygen partial pressure detection sensor unit 80, and the target value of the voltage V0 is controlled so that the gradient of the oxygen partial pressure in the measured gas introduced from the third diffusion rate control unit 30 into the second internal cavity 40 is always constant. When used as a NOx sensor, the oxygen concentration in the second internal cavity 40 is kept at a constant value of about 0.001ppm by the action of the main pump unit 21 and the auxiliary pump unit 50.

The fourth diffusion rate control section 60 is as follows: a predetermined diffusion resistance is applied to the gas to be measured whose oxygen concentration (oxygen partial pressure) is controlled by the operation of the auxiliary pump unit 50 in the second internal cavity 40, and the gas to be measured is guided to the third internal cavity 61. The fourth diffusion rate control portion 60 plays a role of limiting the amount of NOx flowing into the third internal cavity 61.

The third internal cavity 61 is provided as a space for measuring the concentration of nitrogen oxides (NOx) in the gas to be measured, which is introduced through the fourth diffusion rate control section 60 after the oxygen concentration (oxygen partial pressure) has been adjusted in the second internal cavity 40 in advance. The NOx concentration is measured mainly by the operation of the measuring pump unit 41 in the third internal cavity 61.

The measurement pump unit 41 measures the NOx concentration in the measurement target gas in the third internal cavity 61. The measurement pump unit 41 is: an electrochemical pump unit comprising a measurement electrode 44, an outer pump electrode 23, a second solid electrolyte layer 6, a separator 5, and a first solid electrolyte layer 4, wherein the measurement electrode 44 is disposed on the upper surface of the first solid electrolyte layer 4 at a position facing the third internal cavity 61. The measurement electrode 44 is: a porous cermet electrode made of a material having a higher reduction capacity for NOx components in the gas to be measured than the inner pump electrode 22. The measurement electrode 44 also functions as a NOx reduction catalyst that reduces NOx present in the atmosphere in the third internal cavity 61.

The measurement pump unit 41 can suck out oxygen generated by the decomposition of nitrogen oxides in the atmosphere around the measurement electrode 44 to detect the generated amount as the pump current Ip 2.

In order to detect the partial pressure of oxygen around the measurement electrode 44, the first solid electrolyte layer 4, the third substrate layer 3, the measurement electrode 44, and the reference electrode 42 constitute an electrochemical sensor unit, that is, a measurement pump control oxygen partial pressure detection sensor unit 82. The variable power supply 46 is controlled based on the electromotive force (voltage V2) detected by the measurement pump control oxygen partial pressure detection sensor unit 82.

The gas to be measured introduced into the second internal cavity 40 passes through the fourth diffusion rate control section 60 under the condition that the oxygen partial pressure is controlled, and reaches the measurement electrode 44 in the third internal cavity 61. The nitrogen oxide in the gas to be measured around the measurement electrode 44 is reduced (2no→n ₂ +O ₂ ) And oxygen is generated. The generated oxygen is pumped by the measurement pump unit 41, and at this time, the voltage Vp2 of the variable power source 46 is controlled so that the voltage V2 detected by the measurement pump control oxygen partial pressure detection sensor unit 82 is constant (target value). Since the amount of oxygen generated around the measurement electrode 44 is proportional to the concentration of nitrogen oxides in the gas to be measured, the concentration of nitrogen oxides in the gas to be measured is calculated by the pump current Ip2 in the measurement pump unit 41.

The electrochemical sensor unit 83 is constituted by the second solid electrolyte layer 6, the separator 5, the first solid electrolyte layer 4, the third substrate layer 3, the outer pump electrode 23, and the reference electrode 42, and an electromotive force (voltage Vref) can be obtained by the sensor unit 83, and the partial pressure of oxygen in the gas to be measured outside the sensor can be detected by the electromotive force.

The electrochemical reference gas adjustment pump unit 90 is constituted by the second solid electrolyte layer 6, the separator 5, the first solid electrolyte layer 4, the third substrate layer 3, the outer pump electrode 23, and the reference electrode 42. In the reference gas adjustment pump unit 90, a control current (pump current Ip 3) flows due to a control voltage (voltage Vp 3) applied from a power supply circuit 92 connected between the outer pump electrode 23 and the reference electrode 42, and thereby oxygen is pumped. Accordingly, the reference gas adjustment pump unit 90 can suck oxygen from the periphery of the outer pump electrode 23 to the periphery of the reference electrode 42 or suck oxygen from the periphery of the reference electrode 42 to the periphery of the outer pump electrode 23.

In the gas sensor 100 having such a configuration, the measured gas whose oxygen partial pressure is always kept at a constant low value (a value that does not substantially affect the measurement of NOx) by operating the main pump unit 21 and the auxiliary pump unit 50 is supplied to the measurement pump unit 41. Therefore, the concentration of NOx in the measurement target gas can be obtained based on the pump current Ip2, and the pump current Ip2 is approximately proportional to the concentration of NOx in the measurement target gas, and oxygen generated by NOx reduction is sucked out from the measurement pump unit 41 and circulated.

The sensor element 101 further includes a heater portion 70, and the heater portion 70 plays a role of temperature adjustment for heating and maintaining the sensor element 101 so as to improve oxygen ion conductivity of the solid electrolyte. The heater section 70 includes: a heater 72, a heater insulating layer 74, and a pressure release hole 75.

The heater 72 is: a resistor formed so as to be sandwiched between the second substrate layer 2 and the third substrate layer 3 from above and below. The heater 72 is supplied with power from a heater power supply 76 (see fig. 2 and 3) to generate heat, and heats and holds the solid electrolyte forming the sensor element 101.

In addition, the heater 72 is implanted in the entire region of the first to third internal cavities 20 to 61, and the sensor element 101 as a whole can be adjusted to the above-described solid electrolyte activation temperature.

The heater insulating layer 74 is: insulating layers formed on the upper and lower surfaces of the heater 72 by an insulator such as alumina. The heater insulating layer 74 is formed for the purpose of obtaining electrical insulation between the second substrate layer 2 and the heater 72 and electrical insulation between the third substrate layer 3 and the heater 72.

The pressure release hole 75 is: the portion provided so as to penetrate the third substrate layer 3 and the reference gas introduction layer 48 and communicate with the reference gas introduction space 43 is formed for the purpose of alleviating an increase in internal pressure accompanying a temperature increase in the heater insulating layer 74.

A connector electrode 71 is disposed on the rear end side of the sensor element 101. The connector electrode 71 includes: connector electrodes 71a to 71d disposed at the rear end of the upper surface of the sensor element 101, and connector electrodes 71e to 71h disposed at the rear end of the lower surface of the sensor element 101. The connector electrode 71 functions as a terminal for electrically connecting the sensor element 101 to the outside. The connector electrodes 71a to 71e are in one-to-one conduction with the outer pump electrode 23, the inner pump electrode 22, the auxiliary pump electrode 51, the measurement electrode 44, and the reference electrode 42 via leads arranged in the sensor element 101 (see fig. 2). One end of the heater 72 is connected to the connector electrode 71f via an energizing lead 77f disposed inside the sensor element 101. The other end of the heater 72 is connected to the connector electrode 71g via an energizing lead 77g disposed inside the sensor element 101. Since the power feeding lead 77f is schematically illustrated in fig. 2, the power feeding lead 77f includes a conductor in the through hole 73 in fig. 1, although not illustrated. A voltage measurement lead 77h is connected to one end of the heater 72 in parallel with the current-carrying lead 77f, and one end of the heater 72 is connected to the connector electrode 71h via the voltage measurement lead 77 h. Further, as shown in fig. 2, the connector electrode 71f is connected to Ground (GND). The connector electrode 71f is an example of a ground terminal. The potential of Ground (GND) is used as a reference for the potential of the circuit of the control device 95. The Ground (GND) is preferably ground (earth).

As shown in fig. 3, the control device 95 includes: the variable power supplies 24, 46, 52, the power supply circuit 92, the heater power supply 76, the main pump voltage acquisition unit 85, the auxiliary pump voltage acquisition unit 86, the measurement voltage acquisition unit 87, the voltage acquisition unit 88, the reference electrode voltage acquisition unit 89, and the control unit 96.

As shown in fig. 2, the main pump voltage acquisition unit 85 is connected to the connector electrode 71b and the connector electrode 71e via leads, respectively. Thus, the main pump voltage acquisition unit 85 acquires the voltage between the inner pump electrode 22 and the reference electrode 42, that is, the voltage V0 of the above-described main pump control oxygen partial pressure detection sensor unit 80. Similarly, the auxiliary pump voltage acquisition unit 86 is connected to the connector electrode 71c and the connector electrode 71e, respectively, to acquire the voltage V1 between the auxiliary pump electrode 51 and the reference electrode 42 of the auxiliary pump control oxygen partial pressure detection sensor unit 81. The measurement voltage acquisition unit 87 is connected to the connector electrode 71d and the connector electrode 71e, respectively, and acquires the voltage V2 between the measurement electrode 44 and the reference electrode 42 of the measurement pump control oxygen partial pressure detection sensor unit 82. The voltage acquisition unit 88 is connected to the connector electrode 71a and the connector electrode 71e, respectively, to acquire the voltage Vref between the outer pump electrode 23 of the sensor unit 83 and the reference electrode 42.

The reference electrode voltage acquisition unit 89 is connected to the connector electrode 71f and the connector electrode 71e via leads, respectively. Thereby, the reference electrode voltage acquisition unit 89 acquires the voltage Vrg between the connector electrode 71f and the reference electrode 42. Since the connector electrode 71f is connected to the ground as described above, the voltage Vrg acquired by the reference electrode voltage acquisition unit 89 is a voltage between the ground and the reference electrode 42.

As shown in fig. 2, the heater power supply 76 is connected to the connector electrode 71f and the connector electrode 71g via leads, respectively, and supplies power to the heater 72 by applying a voltage between the connector electrodes 71f and 71 g. Since the connector electrode 71f is connected to the ground, the connector electrode 71f is the electrode on the low potential side, and the connector electrode 71g is the electrode on the high potential side. Although the reference electrode voltage acquisition unit 89 and the heater power supply 76 are both connected to the connector electrode 71f, as shown in fig. 2, the connection position between the reference electrode voltage acquisition unit 89 and the connector electrode 71f is closer to the connection position between the heater power supply 76 and the connector electrode 71 f. Therefore, the heater current flowing between the heater power supply 76 and the heater 72 does not flow through the circuit for acquiring the voltage Vrg by the reference electrode voltage acquisition unit 89, that is, the circuit from the connector electrode 71e to the ground.

Although wiring is not shown in fig. 2, the variable power supplies 24, 52, 46, the power supply circuit 92, and the like shown in fig. 1 and 3 are actually connected to the respective electrodes inside the sensor element 101 via the connector electrode 71. As with the voltage acquisition units 85 to 89, the pump currents Ip0, ip1, ip2, ip3 are actually acquired (measured) by unillustrated current acquisition units connected to the electrodes inside the sensor element 101 via the connector electrode 71.

The control unit 96 is: a microprocessor including a CPU97, a memory 98, and the like. The storage unit 98 is a nonvolatile memory capable of rewriting information, and can store various programs and various data, for example. The control unit 96 receives the voltages V0, V1, V2, vref, and Vrg acquired by the voltage acquisition units 85 to 89. The control unit 96 is also supplied with pump currents Ip0, ip1, ip2, ip3 obtained by a current obtaining unit, not shown. The control unit 96 outputs control signals to the variable power supplies 24, 46, 52 and the power supply circuit 92, thereby controlling the voltages Vp0, vp1, vp2, vp3 output from the variable power supplies 24, 46, 52 and the power supply circuit 92, and controlling the main pump unit 21, the measurement pump unit 41, the auxiliary pump unit 50, and the reference gas adjustment pump unit 90. The control unit 96 outputs a control signal to the heater power supply 76, thereby controlling the power supplied from the heater power supply 76 to the heater 72, and adjusting the temperature of the sensor element 101. The storage unit 98 also stores target values V0, V1, V2, etc., which will be described later. The CPU97 of the control unit 96 refers to these target values V0, V1, V2 to control the respective units 21, 41, 50.

The control unit 96 performs an auxiliary pump control process of controlling the auxiliary pump unit 50 so that the oxygen concentration of the second internal cavity 40 reaches the target concentration. Specifically, the control unit 96 performs feedback control of the voltage Vp1 of the variable power source 52 so that the voltage V1 reaches a constant value (referred to as a target value V1), thereby controlling the auxiliary pump unit 50. The target value V1 is determined as: the oxygen concentration in the second internal cavity 40 is a predetermined low concentration value that does not substantially affect the measurement of NOx.

The control unit 96 performs a main pump control process of controlling the main pump unit 21 so that the pump current Ip1 flowing when the oxygen concentration in the second internal cavity 40 is adjusted by the auxiliary pump control process reaches a target current (referred to as target current Ip1 "). Specifically, the control unit 96 sets (feedback-controls) the target value (referred to as target value V0) of the voltage V0 based on the pump current Ip1 so that the pump current Ip1 flowing due to the voltage Vp1 reaches a constant target current Ip 1. The control unit 96 performs feedback control of the voltage Vp0 of the variable power supply 24 so that the voltage V0 reaches the target value v0″ (i.e., so that the oxygen concentration in the first internal cavity 20 reaches the target concentration). By this main pump control process, the gradient of the oxygen partial pressure in the measured gas introduced from the third diffusion rate control section 30 into the second internal cavity 40 is always constant. The target value V0 is set as: the oxygen concentration of the first internal cavity 20 is higher than 0% and takes on such a value as to be low. The pump current Ip0 flowing in the main pump control process changes according to the oxygen concentration of the gas to be measured (i.e., the gas to be measured around the sensor element 101) flowing from the gas inlet 10 into the gas to be measured flowing portion. Therefore, the control unit 96 may also detect the oxygen concentration in the measurement target gas based on the pump current Ip 0.

The above-described main pump control process and auxiliary pump control process are also collectively referred to as an adjustment pump control process. The first internal cavity 20 and the second internal cavity 40 are also collectively referred to as an oxygen concentration adjustment chamber. The main pump unit 21 and the auxiliary pump unit 50 are also collectively referred to as an adjustment pump unit. The control unit 96 performs the adjustment pump control process, and thereby the adjustment pump means adjusts the oxygen concentration in the oxygen concentration adjustment chamber.

The control unit 96 performs a measurement pump control process of controlling the measurement pump unit 41 so that the voltage V2 reaches a constant value (referred to as a target value V2) (i.e., so that the oxygen concentration in the third internal cavity 61 reaches a predetermined low concentration). Specifically, the control unit 96 performs feedback control of the voltage Vp2 of the variable power source 46 so that the voltage V2 reaches the target value v2°, thereby controlling the measurement pump unit 41. By this measurement pump control process, oxygen is sucked out from the third internal cavity 61.

By performing the measurement pump control process, oxygen is sucked out from the third internal cavity 61 so that the oxygen generated by reducing NOx in the measured gas in the third internal cavity 61 becomes substantially zero. The control unit 96 acquires the pump current Ip2 as a detection value corresponding to oxygen generated in the third internal cavity 61 from the specific gas (NOx here), and calculates the NOx concentration in the measured gas based on the pump current Ip 2.

The storage unit 98 stores a relational expression (for example, a formula of a primary function or a quadratic function), a map, and the like as a correspondence relation between the pump current Ip2 and the NOx concentration. Such a relation or map may be found in advance by experiments.

The control unit 96 performs a reference gas adjustment process of controlling the reference gas adjustment pump unit 90 so as to perform oxygen suction from the periphery of the outer pump electrode 23 toward the periphery of the reference electrode 42 or oxygen suction from the periphery of the reference electrode 42 toward the periphery of the outer pump electrode 23. The oxygen concentration around the reference electrode 42 is adjusted by this reference gas adjustment process. In the reference gas adjustment process, the control unit 96 controls the power supply circuit 92 so that the voltage Vp3 is applied to the reference gas adjustment pump unit 90, and the pump current Ip3 flows through the reference gas adjustment pump unit 90. The voltage Vp3 may be a dc voltage such that the pump current Ip3 is a predetermined value (a constant dc current), or may be a voltage (for example, a pulse voltage) that is repeatedly turned on and off. The control unit 96 controls the magnitude of the pump current Ip3 (i.e., the amount of movement of oxygen) and the direction in which the pump current Ip3 flows (i.e., the direction in which the oxygen between the outer pump electrode 23 and the reference electrode 42 moves) by changing the magnitude or the positive and negative of the voltage Vp 3. When the voltage Vp3 is a voltage that is repeatedly turned on and off, the amount of oxygen movement can be adjusted by the ratio of the repeated period T to the on time Ton, that is, the duty ratio (Ton/T). In the present embodiment, the voltage Vp3 is a pulse voltage, and the control unit 96 controls the movement amount and movement direction of oxygen by changing the duty ratio and the positive and negative of the voltage Vp 3. The control unit 96 performs a reference gas adjustment process to adjust the oxygen concentration around the reference electrode 42.

The control unit 96 performs a heater control process of controlling the heater power supply 76 so that the temperature of the heater 72 reaches the target temperature. Since the temperature of the heater 72 can be expressed by a linear function of the resistance value of the heater 72, the control unit 96 controls the heater power supply 76 so that the resistance value of the heater 72 reaches the target resistance value in the heater control process. When the heater control process is started, first, the CPU97 of the control unit 96 controls the heater power supply 76 to start the energization of the heater 72, and causes the heater 72 to generate heat. Then, the CPU97 derives the resistance value of the heater 72 by the 3-terminal method. Specifically, the CPU97 first acquires the first heater voltage Vh1 between the connector electrode 71h and the connector electrode 71g, the second heater voltage Vh2 between the connector electrode 71h and the connector electrode 71f, and the heater current Ih flowing through the heater 72 by the power supplied from the heater power supply 76, by means of a voltage acquisition unit and a current acquisition unit, not shown, provided in the control device 95. Next, the CPU97 derives the heater voltage Vh, which is the voltage across the heater 72 without the voltage drop amounts of the current-carrying lead 77f and the current-carrying lead 77g, using the relational expression of vh=vh 1 to Vh 2. Then, the CPU97 derives the resistance value of the heater 72 by dividing the heater voltage Vh by the heater current Ih. Then, the control unit 96 outputs a control signal to the heater power supply 76 so that the derived resistance value of the heater 72 reaches the target resistance value, and performs feedback control of the power supplied from the heater power supply 76. The heater power supply 76 changes, for example, the value of the voltage applied to the heater 72, thereby adjusting the power supplied to the heater 72.

An example of the NOx concentration detection process performed by the control unit 96 of the gas sensor 100 configured as described above to detect the NOx concentration in the measured gas will be described below. Before starting the NOx concentration detection process, the CPU97 of the control unit 96 first starts the heater control process described above, and controls the temperature of the heater 72 so as to reach the target temperature (for example, 800 ℃). Since the temperature of the heater 72 is also affected by the temperature of the measured gas, the CPU97 continues the heater control process after the start of the NOx concentration detection process. When the temperature of the heater 72 reaches the vicinity of the target temperature, the CPU97 starts the NOx concentration detection process. In the NOx concentration detection process, first, the CPU97 starts the adjustment pump control process and the measurement pump control process, which are the control of the pump units 21, 41, and 50, by acquiring the voltages V0, V1, V2, and Vref from the sensor units 80 to 83. In this state, when the gas to be measured is introduced from the gas inlet 10, the gas to be measured passes through the first diffusion rate control section 11, the buffer space 12, and the second diffusion rate control section 13 in this order, and reaches the first internal cavity 20. Next, the oxygen concentration of the measured gas is adjusted by the main pump unit 21 and the auxiliary pump unit 50 in the first internal cavity 20 and the second internal cavity 40, and the adjusted measured gas reaches the third internal cavity 61. Then, the CPU97 detects the NOx concentration in the measured gas based on the acquired correspondence relationship between the pump current Ip2 and the storage unit 98. The CPU97 transmits the detected value of the NOx concentration to an engine ECU, not shown, and ends the NOx concentration detection process. The CPU97 may perform the NOx concentration detection process at, for example, a timing at which the detection of the NOx concentration is instructed by the engine ECU, or may perform the NOx concentration detection process at a timing at which the detection of the NOx concentration is instructed by the engine ECU.

As is apparent from fig. 2, the voltages V0 to V2 and Vref detected by the voltage acquisition units 85 to 88 of the control device 95 are voltages between the reference electrode 42 and the electrodes 22, 51, 44, and 23. The reference potential, which is the potential of the reference electrode 42, is a value corresponding to the oxygen concentration around the reference electrode 42. Since the reference gas is introduced into the reference electrode 42 via the reference gas introduction portion 49, if the oxygen concentration of the reference gas is constant, the oxygen concentration around the reference electrode 42 is substantially constant. However, in reality, the oxygen concentration around the reference electrode 42 may vary during use of the sensor element 101. For example, in the gas sensor 100, the periphery of the front end side and the periphery of the rear end side of the sensor element 101 are sealed by a sensor assembly or the like, not shown, so that the gas to be measured existing in the periphery of the front end side of the sensor element 101 and the reference gas existing in the periphery of the rear end side of the sensor element 101 do not flow through each other. However, when the pressure of the gas to be measured is high, the gas to be measured may slightly intrude into the reference gas, and the oxygen concentration around the reference electrode 42 may be reduced. In addition, while the sensor element 101 is not driven, external water may be adsorbed by the reference gas introduction portion 49, and when the driving is started, the sensor element 101 is heated, and the water in the reference gas introduction portion 49 turns into gas and escapes to the outside of the sensor element 101, but in the period until the water escapes, the oxygen concentration around the reference electrode 42 may be reduced due to the presence of the gas. If the oxygen concentration around the reference electrode 42 changes in this way, the reference potential of the reference electrode 42 deviates, and the values of the voltages V0 to V2 and Vref also change, so that the accuracy of detecting the NOx concentration decreases.

Therefore, in the gas sensor 100 according to the present embodiment, the control unit 96 performs reference potential adjustment processing, that is, adjusts the reference potential by grasping the deviation of the reference potential of the reference electrode 42. Fig. 4 is a flowchart showing an example of the reference potential adjustment processing routine executed by the control unit 96. The control unit 96 stores the routine in, for example, the storage unit 98. The control unit 96 repeatedly executes this routine, for example, every time a predetermined time elapses.

When the reference potential adjustment processing routine is started, the CPU97 of the control section 96 first inputs the voltage Vrg acquired by the reference electrode voltage acquisition section 89 (step S100). That is, the CPU97 measures the voltage Vrg between the ground and the reference electrode 42. Since the potential of ground is substantially constant, the voltage Vrg is a value corresponding to the oxygen concentration around the reference electrode 42. Next, the CPU97 compares the value of the inputted voltage Vrg with a predetermined allowable range of the voltage Vrg, and determines whether the voltage Vrg is within the allowable range (step S110). The predetermined allowable range is predetermined to include a normal value of the voltage Vrg and a value close to the normal value, and is stored in the storage unit 98. The normal value of the voltage Vrg is: for example, the value of the voltage Vrg when the oxygen concentration around the reference electrode 42 coincides with the normal oxygen concentration of the reference gas (here, the oxygen concentration of the atmosphere). The upper and lower limits of the allowable range may be determined in advance based on the upper and lower limits of the range of the voltage Vrg in which the deviation of the reference potential can be tolerated, in other words, the upper and lower limits of the allowable range of the oxygen concentration around the reference electrode 42, because the influence on the measurement accuracy of the NOx concentration is small, for example. The process of determining whether the voltage Vrg is within the allowable range corresponds to a process of grasping the deviation of the reference potential. The difference between the normal value and the upper and lower limits of the allowable range of the voltage Vrg corresponds to the upper and lower limits of the allowable range of the deviation of the reference potential. Since the difference between the measured voltage Vrg and the normal value or the ratio thereof is a value indicating the deviation of the reference potential, the CPU97 can compare the difference or the ratio with the allowable range of the difference or the ratio to determine in step S110. In the present embodiment, the voltage Vrg is defined as the potential of the reference electrode 42 with respect to the ground, and the voltage Vrg is a positive value regardless of the magnitude of the oxygen concentration around the reference electrode 42. However, for example, the voltage Vrg may be defined as a negative value, and in this case, the absolute value of the voltage Vrg may be compared with the allowable range of the voltage Vrg.

On the other hand, in step S110, when the voltage Vrg is greater than the allowable range, that is, when the reference potential is deviated such that the oxygen concentration around the reference electrode 42 is higher than the upper limit of the allowable range, the CPU97 controls the reference gas adjustment pump unit 90 so as to suck oxygen from the periphery of the reference electrode 42 to the periphery of the outer pump electrode 23 (step S120). Accordingly, the oxygen concentration around the reference electrode 42 is reduced, so that the voltage Vrg can be set within the allowable range. That is, when the reference potential of the reference electrode 42 is deviated to a value higher than the upper limit of the allowable range, the CPU97 controls the reference gas adjustment pump unit 90 so as to lower the reference potential to be within the allowable range.

In step S110, when the voltage Vrg is smaller than the allowable range, that is, when the deviation of the reference potential occurs such that the oxygen concentration around the reference electrode 42 is lower than the lower limit of the allowable range, the CPU97 controls the reference gas adjustment pump unit 90 so as to suck oxygen from the periphery of the outer pump electrode 23 to the periphery of the reference electrode 42 (step S130). Accordingly, the oxygen concentration around the reference electrode 42 increases, so that the voltage Vrg can be set within the allowable range. That is, when the reference potential of the reference electrode 42 is deviated to a value lower than the lower limit of the allowable range, the CPU97 controls the reference gas adjustment pump unit 90 so as to raise the reference potential to be within the allowable range.

In step S110, when the voltage Vrg is within the allowable range, that is, when the reference potential is deviated from the allowable range, the CPU97 ends the routine. The CPU97 also ends the present routine after the execution of step S120 or after the execution of step S130.

By executing this reference potential adjustment processing routine, the oxygen concentration around the reference electrode 42 is adjusted based on the determination result of step S110 (i.e., the result of grasping the deviation of the reference potential) so that the deviation of the reference potential from the normal value becomes small, and therefore, it is possible to suppress a decrease in the detection accuracy of the NOx concentration caused by the deviation of the reference potential. In the present embodiment, as described above, the CPU97 changes the duty ratio of the voltage Vp3 as the pulse voltage to adjust the amount of oxygen sucked out in step S120 and the amount of oxygen sucked in step S130. The CPU97 determines the suction amount as: for example, the larger the difference between the value of the voltage Vrg input in step S100 and the normal value of the voltage Vrg or the ratio (i.e., the deviation amount of the reference potential) is, the larger the value is. In other words, the CPU97 may determine the control amount (here, the duty ratio of the voltage Vp 3) of the reference gas adjustment pump unit 90 in step S120 and step S130 as: a value corresponding to the amount of movement of oxygen required to change the value of the voltage Vrg input in step S100 to a normal value or a value close to the normal value. The correspondence between the value of the voltage Vrg input in step S100 and the control amount of the reference gas adjustment pump unit 90, or the correspondence between the ratio of the difference between the voltage Vrg and the normal value or the control amount of the reference gas adjustment pump unit 90 is determined in advance and stored in the storage unit 98, and the cpu97 can determine the control amount of the reference gas adjustment pump unit 90 based on the correspondence. The control amount of the reference gas adjustment pump unit 90 may be a magnitude of the voltage Vp3 instead of or in addition to the duty ratio of the voltage Vp3, and the operation time of the reference gas adjustment pump unit 90 may be adjusted. That is, the CPU97 may adjust the amount of movement of oxygen according to the magnitude of the voltage Vp3, or may adjust the amount of movement of oxygen according to the length of the operation time of the reference gas adjustment pump unit 90.

The amount of oxygen suctioned in step S120 and the amount of oxygen suctioned in step S130 may be constant values. In this case, the voltage Vrg can be set within the allowable range by repeatedly executing the reference potential adjustment processing routine, and therefore, the deviation of the reference potential can be reduced. In this case, the CPU97 repeatedly executes the reference potential adjustment processing routine to repeatedly perform measurement of the voltage Vrg and control of the reference gas adjustment pump unit 90 until the voltage Vrg is within the allowable range.

The voltage Vrg in step S100 is preferably measured at a timing when the pump current Ip3 does not flow through the reference electrode 42. Accordingly, the voltage drop amount due to the pump current Ip3 can be suppressed from being included in the voltage Vrg, and the voltage Vrg can be a more accurate value corresponding to the oxygen concentration around the reference electrode 42. For example, when the voltage Vp3 is a pulse voltage, the CPU97 preferably measures the voltage Vrg while the voltage Vp3 is off. Alternatively, the CPU97 may control the power supply circuit 92 so that the voltage Vp3 is not applied when the voltage Vrg is measured. The same applies to the measurement of the voltages V0 to V2 and Vref.

Here, the correspondence between the components of the present embodiment and the components of the present invention will be clarified. The sensor element 101 of the present embodiment corresponds to the sensor element of the present invention, the stacked body in which 6 layers of the first substrate layer 1, the second substrate layer 2, the third substrate layer 3, the first solid electrolyte layer 4, the separator 5, and the second solid electrolyte layer 6 are stacked in this order corresponds to the element body, the third internal cavity 61 corresponds to the measurement chamber, the measurement electrode 44 corresponds to the measurement electrode, the reference electrode 42 corresponds to the reference electrode, and the control device 95 corresponds to the control device. The outer pump electrode 23 corresponds to the gas side electrode to be measured and the outer measuring electrode, the voltage V2 corresponds to the measuring voltage, and the target value v2_corresponds to the measuring voltage target value. The first internal cavity 20 and the second internal cavity 40 correspond to oxygen concentration adjustment chambers, the auxiliary pump electrode 51 corresponds to inner adjustment electrodes, the main pump unit 21 and the auxiliary pump unit 50 correspond to adjustment pump units, the voltage V1 corresponds to adjustment voltage, the target value V1 corresponds to adjustment voltage target value, the connector electrode 71f corresponds to a ground terminal, and the heater 72 corresponds to a heater. In the present embodiment, the operation of the gas sensor 100 will be described, and thus, an example of a method for grasping the deviation of the reference potential of the gas sensor according to the present invention will be apparent.

According to the gas sensor 100 of the present embodiment described above, the control device 95 measures the voltage Vrg between the ground and the reference electrode 42, and grasps the potential of the reference electrode 42, that is, the deviation of the reference potential, based on the voltage Vrg. Since the voltage Vrg changes with the change in the oxygen concentration around the reference electrode 42, that is, the change in the reference potential, the deviation of the reference potential can be grasped based on the voltage Vrg.

The sensor element 101 includes a reference gas adjustment pump unit 90, and includes: the pump electrode 23 and the reference electrode 42 are provided on the outside of the element body so as to be in contact with the gas to be measured. When the measured voltage Vrg is greater than the allowable range, the control device 95 controls the reference gas adjustment pump unit 90 so as to suck oxygen from the periphery of the reference electrode 42 to the periphery of the outer pump electrode 23. When the measured voltage Vrg is smaller than the allowable range, the reference gas adjustment pump unit 90 is controlled so that oxygen is sucked from the periphery of the outer pump electrode 23 to the periphery of the reference electrode 42. Accordingly, the oxygen concentration around the reference electrode 42 can be adjusted according to the deviation of the reference potential, and therefore, the deviation of the reference potential can be made small, and the decrease in the detection accuracy of the NOx concentration caused by the deviation of the reference potential can be suppressed. Here, the reference gas adjustment pump unit 90 is also conventionally used to adjust the oxygen concentration around the reference electrode 42, but the voltage Vrg between the ground and the reference electrode 42 is not used to grasp the deviation of the reference potential. Therefore, the amount of movement of oxygen by the reference gas adjustment pump unit 90 may be too large or insufficient, and the oxygen concentration around the reference electrode 42 may not be maintained in an appropriate state (normal oxygen concentration of the reference gas). In the gas sensor 100 of the present embodiment, the CPU97 controls the reference gas adjustment pump unit 90 based on the deviation of the reference potential grasped by the voltage Vrg, and therefore, the reference gas adjustment pump unit 90 can be controlled more appropriately, and the oxygen concentration around the reference electrode 42 can be easily maintained in an appropriate state.

The present invention is not limited to the above embodiments, and may be implemented in various forms as long as the present invention is within the technical scope of the present invention.

In the above embodiment, the control device 95 adjusts the oxygen concentration around the reference electrode 42 based on the comparison between the measured voltage Vrg and the allowable range, that is, the result of grasping the deviation of the reference potential, but is not limited thereto. For example, the control device 95 may correct the control of each of the pump units 21, 50, 41 based on the deviation of the grasped reference potential. Fig. 5 is a flowchart showing an example of the control correction process. The control unit 96 stores the routine in, for example, the storage unit 98. The control unit 96 repeatedly executes this routine, for example, every time a predetermined time elapses. When the control correction processing routine is started, the CPU97 of the control unit 96 performs the same processing as in step S100 of the reference potential adjustment processing described above, and measures the voltage Vrg. Next, the CPU97 calculates a difference Δvrg (=measurement value-normal value) between the measurement value and the normal value of the voltage Vrg (step S210). Then, the CPU97 corrects the control of each pump unit 21, 50, 41 based on the difference Δvbg (step S220), and ends the present routine. The correction of the control of each pump unit 21, 50, 41 may be, for example, correction of a measured value of the voltage related to the control, or correction of a target value of the voltage related to the control. Since the difference Δvbg corresponds to the amount of deviation of the reference potential, the influence of the deviation of the reference potential can be canceled by correcting the measured value or the target value of the voltage associated with the control of each of the pump units 21, 50, 41 based on the difference Δvbg, and control substantially similar to the case where there is no deviation of the reference potential can be performed. For example, in the above embodiment, since the oxygen concentration around each electrode 22, 51, 44 is lower than the oxygen concentration around the reference electrode 42, when the reference potential of the reference electrode 42 is deviated in a direction higher than the normal value (the difference Δvrg is positive), the voltages V0 to V2 measured by each of the voltage acquisition units 85 to 87 are measured as values deviated in a direction in which the absolute value becomes larger. When the reference potential of the reference electrode 42 is deviated in a direction lower than the normal value (the difference Δvrg is negative), the voltages V0 to V2 measured by the respective voltage acquisition units 85 to 87 are measured as values deviated in a direction in which the absolute value becomes smaller. Therefore, the CPU97 calculates the corrected voltages V0 to V2 as the absolute values of the measured values of the voltages V0 to V2 acquired by the voltage acquisition units 85 to 87 minus the difference Δvrg. Then, the CPU97 compares the corrected voltages V0 to V2 with the target values V0 to V2, and performs the adjustment pump control process and the measurement pump control process. Alternatively, the CPU97 may calculate the absolute value of the target values V0 to V2 plus the difference DeltaVrg as the corrected target values V0 to V2. In this case, the CPU97 compares the measured values of the voltages V0 to V2 with the corrected target values V0 to V2, and performs the adjustment pump control process and the measurement pump control process. The CPU97 updates the correction amount (i.e., the difference Δvrg) of the adjustment pump control process and the measurement pump control process every time the step S220 of the control correction process is executed. The correction based on the deviation of the reference potential may be performed with respect to at least one of the adjustment pump control process and the measurement pump control process, or may be performed with respect to at least one of the main pump control process, the auxiliary pump control process, and the measurement pump control process. However, since the measurement pump control process is the one that has the greatest influence on the accuracy of measuring the NOx concentration, when the control correction process of fig. 5 is performed, it is preferable that the CPU97 perform at least the correction based on the deviation of the reference potential as described above on the measurement pump control process. In the case where the oxygen concentration in the gas to be measured is detected based on the voltage Vref acquired by the voltage acquisition unit 88, the CPU97 may perform the correction similar to the correction of the voltages V0 to V2 described above also on the voltage Vref in step S220.

In the above embodiment, the gas sensor 100 may not include the reference gas adjustment pump unit 90 and the power supply circuit 92. In this case, the control unit 96 can also perform the control correction processing of fig. 5.

In the above embodiment, the voltage Vrg is set to the voltage between the connector electrode 71f and the reference electrode 42, which is the terminal of the heater 72, but is not limited thereto. For example, the voltage Vrg may be a voltage between a terminal connected to the ground and the reference electrode 42 of the sensor element 101, and is not limited to a voltage between a terminal of the heater 72 and the reference electrode 42. The voltage between the ground and the reference electrode 42 may be measured, not limited to the terminal provided in the sensor element 101. For example, the voltage between the reference electrode 42 and the other ground which is not connected to all the connector electrodes 71 in the sensor element 101 may be measured, and the deviation of the reference potential may be grasped based on the voltage. The inventors of the present invention confirmed by experiments that: not limited to the voltage Vrg of the above embodiment, the voltage between the reference electrode 42 and the other ground which is not connected to all the connector electrodes 71 of the sensor element 101 is also changed in accordance with the change in the oxygen concentration around the reference electrode 42, and the deviation of the reference potential can be grasped based on the voltage.

In the reference potential adjustment process of fig. 5, the CPU97 controls the reference gas adjustment pump unit 90 based on the grasp of the deviation of the reference potential based on the voltage Vrg (step S110) (steps S120 and S130), and in the control correction process of fig. 6, the CPU corrects the control of each pump unit 21, 50, 41 based on the grasp of the deviation of the reference potential based on the voltage Vrg (step S210) (step S220), but the present invention is not limited thereto. For example, the CPU97 may report a reference potential abnormality when the deviation of the reference potential is beyond the allowable range, which has been grasped, for example, when the negative determination is made in step S110 or when the difference Δvrg calculated in step S210 is not within the allowable range. For example, the CPU97 may output a signal reporting the abnormality of the reference potential to the engine ECU. In this way, the CPU97 can perform only diagnosis of the deviation of the reference potential.

In the above embodiment, the reference gas introduction portion 49 includes the reference gas introduction space 43 and the reference gas introduction layer 48, but the reference gas introduction portion 49 may be capable of introducing the reference gas to the reference electrode 42 from outside the sensor element 101. For example, the reference gas introduction portion 49 may include at least one of the reference gas introduction space 43 and the reference gas introduction layer 48.

In the above embodiment, the gas sensor 100 detects the NOx concentration as the specific gas concentration, but the present invention is not limited to this, and other oxide concentrations may be set to the specific gas concentration. In the case where the specific gas is an oxide, similarly to the above embodiment, since oxygen is generated when the specific gas itself is reduced in the third internal cavity 61, the CPU97 can acquire a detection value corresponding to the oxygen to detect the specific gas concentration. The specific gas may be a non-oxide such as ammonia. In the case where the specific gas is a non-oxide, the specific gas is converted into an oxide (for example, into NO if ammonia) so that the converted gas generates oxygen upon reduction of the third internal cavity 61, and therefore, the CPU97 can acquire a detection value corresponding to the oxygen to detect the specific gas concentration. In this way, the gas sensor 100 is able to detect the specific gas concentration based on oxygen that originates from the specific gas and is generated in the third internal cavity 61, whether the specific gas is an oxide or a non-oxide.

In the above embodiment, the sensor element 101 of the gas sensor 100 includes the first internal cavity 20, the second internal cavity 40, and the third internal cavity 61, but is not limited thereto. For example, the third internal cavity 61 may not be provided like the sensor element 201 of fig. 6. In the sensor element 201 of the modification shown in fig. 6, the gas introduction port 10, the first diffusion rate control portion 11, the buffer space 12, the second diffusion rate control portion 13, the first internal cavity 20, the third diffusion rate control portion 30, and the second internal cavity 40 are formed adjacent to each other so as to be sequentially communicated in this order between the lower surface of the second solid electrolyte layer 6 and the upper surface of the first solid electrolyte layer 4. The measurement electrode 44 is disposed on the upper surface of the first solid electrolyte layer 4 in the second internal cavity 40. The measurement electrode 44 is covered with a fourth diffusion rate control section 45. The fourth diffusion rate control portion 45 is made of alumina (Al ₂ O ₃ ) And a membrane made of a ceramic porous body. The fourth diffusion rate control unit 45 plays a role of limiting the amount of NOx flowing into the measurement electrode 44, similarly to the fourth diffusion rate control unit 60 of the above embodiment. The fourth diffusion rate control unit 45 also serves as a measurement power sourceThe protective film of pole 44 functions. The top electrode portion 51a of the auxiliary pump electrode 51 is formed directly above the measurement electrode 44. Even with the sensor element 201 having such a configuration, the NOx concentration can be detected based on, for example, the pump current Ip2 as in the above-described embodiment. In this case, the periphery of the measurement electrode 44 functions as a measurement chamber.

In the above embodiment, the element body of the sensor element 101 is a laminate having a plurality of solid electrolyte layers (layers 1 to 6), but is not limited thereto. The element body of the sensor element 101 may have at least 1 oxygen ion conductive solid electrolyte layer, and the measured gas flow portion may be provided inside. For example, in fig. 1, the layers 1 to 5 other than the second solid electrolyte layer 6 may be structural layers (for example, layers made of alumina) made of materials other than the solid electrolyte. In this case, each electrode of the sensor element 101 may be disposed on the second solid electrolyte layer 6. For example, the measurement electrode 44 in fig. 1 may be disposed on the lower surface of the second solid electrolyte layer 6. In addition, the reference gas introduction space 43 may be provided in the separator 5 instead of the first solid electrolyte layer 4, the reference gas introduction layer 48 may be provided between the second solid electrolyte layer 6 and the separator 5 instead of between the first solid electrolyte layer 4 and the third substrate layer 3, and the reference electrode 42 may be provided on the lower surface of the second solid electrolyte layer 6 rearward of the third internal cavity 61.

In the above embodiment, the control unit 96 sets (feedback-controls) the target value v0_of the voltage V0 based on the pump current Ip1 so that the pump current Ip1 reaches the target current Ip 1_and feedback-controls the pump voltage Vp0 so that the voltage V0 reaches the target value v0_however, other control may be performed. For example, the control unit 96 may perform feedback control of the pump voltage Vp0 based on the pump current Ip1 so that the pump current Ip1 reaches the target current Ip 1. That is, the control unit 96 may omit acquiring the voltage V0 or setting the target value V0 from the main pump control oxygen partial pressure detection sensor unit 80, and directly control the pump voltage Vp0 based on the pump current Ip1 (or even control the pump current Ip 0).

In the above embodiment, the oxygen concentration adjustment chamber has the first internal cavity 20 and the second internal cavity 40, but the oxygen concentration adjustment chamber is not limited thereto, and for example, the oxygen concentration adjustment chamber may further have another internal cavity, or one of the first internal cavity 20 and the second internal cavity 40 may be omitted. Similarly, in the above-described embodiment, the adjustment pump unit includes the main pump unit 21 and the auxiliary pump unit 50, but the present invention is not limited thereto, and for example, the adjustment pump unit may further include another pump unit, and one of the main pump unit 21 and the auxiliary pump unit 50 may be omitted. For example, in the case where the oxygen concentration of the measurement target gas can be sufficiently reduced by only the main pump unit 21, the auxiliary pump unit 50 may be omitted. When the auxiliary pump unit 50 is omitted, the control unit 96 may perform only the main pump control process as the adjustment pump control process. In the main pump control process, the setting of the target value V0 based on the pump current Ip1 is omitted. Specifically, the control unit 96 may control the main pump unit 21 by storing a predetermined target value v0+ in the storage unit 98 in advance and performing feedback control on the voltage Vp0 of the variable power supply 24 so that the voltage V0 reaches the target value v0+. When the auxiliary pump unit 50 is omitted, the inner pump electrode 22 corresponds to an inner adjustment electrode, the voltage V0 corresponds to an adjustment voltage, and the target value v0_corresponds to an adjustment voltage target value.

In the above embodiment, the outer pump electrode 23 doubles as: the present invention is not limited to the outer main pump electrode that is a part of the main pump unit 21 and is disposed on the outer side of the sensor element 101 and is exposed to the gas to be measured, the outer auxiliary pump electrode that is a part of the auxiliary pump unit 50 and is disposed on the outer side of the sensor element 101 and is exposed to the gas to be measured, the outer measurement electrode that is a part of the measurement pump unit 41 and is disposed on the outer side of the sensor element 101 and is exposed to the gas to be measured, and the gas to be measured side electrode that is a part of the reference gas adjustment pump unit 90 and is disposed on the outer side of the sensor element 101 and is exposed to the gas to be measured. Any one or more of the outer main pump electrode, the outer auxiliary pump electrode, the outer measurement electrode, and the measured gas side electrode may be separately provided outside the sensor element 101, unlike the outer pump electrode 23. The measured gas side electrode of the reference gas adjustment pump unit 90 may be provided on the sensor element 101 so as to be in contact with the measured gas, and may be disposed, for example, not limited to the outside of the sensor element 101, but may be disposed on the inside thereof, more specifically, may be disposed on the measured gas flow portion of the sensor element 101. For example, the inner pump electrode 22 serves as both the electrode of the main pump unit 21 (inner main pump electrode) and the measured gas side electrode of the reference gas adjustment pump unit 90, and the reference gas adjustment pump unit 90 can perform suction or extraction of oxygen between the periphery of the inner pump electrode 22 and the periphery of the reference electrode 42.

Japanese patent application No. 2022-125272, filed on 5/8/2022, is hereby incorporated by reference in its entirety herein as if set forth at the basis of priority.

Industrial applicability

The present invention can be used in a gas sensor for detecting the concentration of a specific gas such as NOx in a measured gas such as an automobile exhaust gas.

Claims

1. A gas sensor includes a sensor element and a control device for detecting a specific gas concentration in a gas to be measured, that is, a specific gas concentration,

the gas sensor is characterized in that,

the sensor element is provided with:

2. A gas sensor according to claim 1, wherein,

the sensor element includes a reference gas adjustment pump unit configured to include: a gas-to-be-measured side electrode provided to the element body so as to be in contact with the gas to be measured, and the reference electrode,

the control device controls the reference gas adjustment pump unit so as to suck oxygen from the periphery of the reference electrode to the periphery of the measured gas side electrode when the measured voltage is greater than the allowable range, and controls the reference gas adjustment pump unit so as to suck oxygen from the periphery of the measured gas side electrode to the periphery of the reference electrode when the measured voltage is less than the allowable range.

3. A gas sensor according to claim 1 or 2, wherein,

the sensor element includes a measurement pump unit configured to include: an outer measurement electrode provided outside the element body so as to be in contact with the gas to be measured, and the measurement electrode,

The control device performs a measurement pump control process of controlling the measurement pump unit so that a voltage between the measurement electrode and the reference electrode, that is, a measurement voltage reaches a measurement voltage target value, and detects the specific gas concentration in the measured gas based on a pump current flowing through the measurement pump unit due to the measurement pump control process,

the control device corrects the control of the measurement pump unit in the measurement pump control process based on the deviation of the grasped reference potential.

4. A gas sensor according to claim 3, wherein,

the sensor element includes an adjustment pump unit configured to include: an inner adjustment electrode disposed in an oxygen concentration adjustment chamber located upstream of the measurement chamber in the measured gas flow portion, the inner adjustment electrode being configured to adjust an oxygen concentration of the oxygen concentration adjustment chamber,

the control device performs an adjustment pump control process in which the adjustment pump unit is controlled to adjust the oxygen concentration in the oxygen concentration adjustment chamber so that the voltage between the inner adjustment electrode and the reference electrode, that is, the adjustment voltage, reaches an adjustment voltage target value,

The control device corrects the control of the adjustment pump unit in the adjustment pump control process based on the deviation of the grasped reference potential.

5. A gas sensor according to claim 1 or 2, wherein,

the sensor element is provided with a ground terminal connected to the ground,

the control device measures a voltage between the ground terminal and the reference electrode as a voltage between the ground and the reference electrode.

6. A gas sensor according to claim 5, wherein,

the sensor element is provided with a heater for heating the element body,

the ground terminal is a terminal of the heater.

7. A method for grasping the deviation of a reference potential of a gas sensor for detecting the concentration of a specific gas among gases to be measured, that is, the specific gas concentration,

the method for grasping the deviation of the reference potential of the gas sensor is characterized in that,

the gas sensor is provided with a sensor element,

the sensor element is provided with:

A measurement electrode disposed in the measured gas flow section; and

the method for grasping the deviation of the reference potential of the gas sensor includes the steps of: and measuring a voltage between the ground and the reference electrode, and grasping a potential of the reference electrode, that is, a deviation of the reference potential, based on the measured voltage.